respiratory symptoms, but influenza does not involve the gastrointestinal tract.

The term stomach flu presumes a viral infection, even though there may be other causes of infection.

Viral infections are the most common cause of gastroenteritis; but bacteria, parasites, and food-borne illnesses (such as from shellfish that has been contaminated by sewage or from consuming raw or undercooked shellfish from contaminated water) can also be the offending agents. Many people who experience vomiting and diarrhea that develops from these types of infections or irritations think they have "food poisoning," when they actually may have a food-borne illness.

The severity of infectious gastroenteritis depends on the immune system's ability to resist the infection. Electrolytes (these include essential chemicals like sodium, potassium and chloride) may be lost in vomit and diarrhea fluid.

Most people recover easily from a short episode of vomiting and diarrhea by drinking clear fluids to replace the fluid that was lost and then gradually progressing to a normal diet. But for others, especially infants and the elderly, the loss of bodily fluid with gastroenteritis can cause dehydration, which can be a life-threatening illness unless it is treated and fluids in the body are replaced.

The most recent data from the CDC show that deaths from gastroenteritis have increased dramatically. In 2007, 17,000 people died from gastroenteritis, overwhelmingly, these people were older and the most common infections were Clostridium difficile and norovirus.

Gastroenteritis Causes

Gastroenteritis has many causes. Viruses and bacteria are the most common.

Viruses and bacteria can be contagious and can spread through the consumption of contaminated food or water. In up to 50% of diarrheal outbreaks, no specific agent is found. The infection can spread from person to person because of improper handwashing following a bowel movement or handling a soiled diaper.

Gastroenteritis caused by viruses may last one to two days. However, some bacterial cases can continue for months.

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